Inductive digital encoders



PIC-3.2

' United States Patent United States Patent Officc 3,003,145. Patented Oct. 3, 1961 3,003,145 INDUCIIVE DIGITAL ENCODHIS Gunther Wolff, Westport, Conn, asslgnol' '1 Automation, Inc, Sonthpol'l, Conn. Filed amuse, Ser. No. 837,850 3 (Cl. M7)

This invention relates to improvements in the design of inductive digital encoders (the latter disclosed in 2,942,252, dated June 21, 1960. More specifically the invention relates to an improved digital en er which is employed to convert the position of a member in space into electrically coded, numerical values; furthermore mechanical-electrical transducing is accomplished by a two stationary pick-oi! core in conjunction with a magnetically codified movable member.

Inductive digital encoders as disclosed in the above referenced application perform well unless a considerable amount of resolution in a small unit is desired. It then becomes difiicult to provide a sufliciently narrow pick-off core and still maintain an acceptable signal-to-noise ratio,

as well as a large signal output level.

It is therefore an object of this invention to provide an inductive digital encoder capable of high resolution and of small size.

It is a further object of this invention to provide an inductive digital encoder capable of yielding a large signal output level even for high resolution and small size.

One feature of the invention is to provide a plurality of narrow pick-off cores, all surrounded by common exciting and pick-off coils and separated by a distance equal to approximately one quantum. 'Ihis feature permits the maintaining of a sufiicient magnetic area at the air gap for high total flux flow despite the narrowing down of each individual pick-ofi core. Furthermore this objective is achieved without presenting large additional surfaces from which magnetic leakage to the surrounding metal could take place.

Another feature of the invention is to provide a magnetic shield around the pick-off coils so as to leakage off the pick-o6 core by'creating a magnetically equi-potential surface near said core.

Another feature of the invention is to provide electrically conductive material at the tip of the cores and adiacent to said cores, so as to minimize leakage flux by creating an area of high magnetic reluctance as a consequence of the eddy currents in said electrically conductive portions.

The above as well as other of the invention will become apparent from the following specification and accompanying drawings in which: FIGURE 1 is a partial plan view of the codified movable member of an inductive digital encoder to which the principles of the improvements of this invention have been applied.

FIGURE 2. is a sectional elevation view taken along line 2-2 of FIGURE 1.

FIGURE 3 is a bottom view Referring to FIGURES 1-3,

objects and novel features W. and particularly to FIG toMachine.

.ingandpick-oflcoils URE 2, the pick-off core I is several quanta wide, as becomes apparent from the fact that more than one raised portion of the codified movable member 2 is subtended by the outer confines of said pick-off core 1. The tip portion of saidpick-oif core 1 is, howeve slotted so as to result in intimate magnetic contact between movable member and core only for each quantum of rotation of the movable member. It is permissible to repeat such pick-01f projections at points of redundancy on the codified movable'member because of the repetitiveness of digital codes.

FIGURE 2 further shows a pick-off coil 3 which may extend for a considerable distance parallel to the pick-cl! core. Said pick-off coil is surrounded by a magnetic shield 4 which is prevented from conducting any appreciable flux to the codified movable member by means of the air gap 5 which is large compared to the main air gap 6. The shield 4 is essentially at the same magnetic potential as the core 1 since they are both subject to the exciting coil 7. Thus little magnetic flux flows from core 1 to shield 4 and therefore the undesired voltage induced in pick-0E coil 3 due to such leakage flux is Each pick-off pro on 8 is surrounded on its two long sides by bars of electrically conductive material 9. Any flux that would tend to leak from pick-off core to the codified movable member through these said electrically conductive bars would induce an eddy current in said bars. This eddy current would set up a counter magneto-motive force which would tend to reduce the flux.

What is claimed is:

1. In an inductive digital encoder, signal sensing means comprising inductively related exciting and pick-off coils whose inductive rel n is varied by a movable magnetic member; and a magnetic shield extending from inside said exciting coil to outside said pick-oi! coil.

2. In an inductive digital encoder signal sensing means comprising inductively related exciting and pick-off coils wound over a core with a pluralitybatgl projections near on said pick-off core,

member.

3. Inaninduetivedigital'encodersignalsenaing comprising inductively related excitinl and pick-0E coils wound overacorewithaplurality of projectionsnearita tip;amagneticahieldextendingfromimidesaidexciting coil tooutside saidpick-otf coil; andelectrically conductingbarsadiaeentto y with thewidthoftheprojeetionsonsaidpiek-otfeore,theinductiverelationofsaidexcitingandpick-oflooilabeinl varied by a movable magnetic member.

usreaeslfltstlintheflleofthispatent UNI'IEDS'IA'I'ESPATBN'I'S 

